Qimiao Si is the Harry C. and Olga K. Wiess Professor of Physics and Astronomy at Rice University. He came to the United States through the highly selective CUSPEA program in 1986, upon earning his B.S. in Physics from University of Science and Technology of China. He received his Ph.D. in Physics in 1991 from the University of Chicago and subsequently did postdoctoral work at Rutgers University and University of Illinois at Urbana-Champaign. He has been on the faculty of Rice University since 1994 (making the actual move to Rice in 1995, after a year's leave of absence).

Prof. Si works in the field of theoretical condensed matter physics. His major contributions have been in the area of strongly correlated electron systems, including quantum criticality and emergent quantum phases, magnetic heavy fermion metals, high temperature superconductors, and mesoscopic and disordered electronic systems.

He is particularly well known for his contributions to the theory of quantum criticality, which concerns the physics of matter undergoing a transition from one quantum state to another. He introduced and developed the theory of local quantum criticality, which involves the notion of critical destruction of Kondo entanglement. The theory goes beyond the Landau framework, and has received extensive support from experiments in magnetic heavy fermion systems. He has made seminal contributions to the young field of iron-pnictides superconductors, contributing broadly to the understanding of electron correlations, quantum criticality, magnetism and superconductivity. He has introduced the Bose-Fermi Kondo model and the method of the extended dynamical mean field theory, and contributed to the early development of the dynamical mean field theory. Other topics he has studied include the spin dynamics of the high temperature cuprate superconductors, metal-insulator transition in disordered and interacting electrons in two dimensions, experimental signatures of spin-charge separation, non-Fermi liquid states in an extended Hubbard model and in quantum impurity systems, and Mott transition between metallic and correlated insulating phases of interacting electrons.

Prof. Si was named a Sloan Research Fellow in 1996, and received a Cottrell Scholar Award from the Research Corporation for Science Advancement in 1998. He was elected a Fellow of the British Institute of Physics in 2004, the American Physical Society in 2005, and the American Association for the Advancement of Science in 2008. He received a Humboldt Prize from the Alexander von Humboldt Foundation in 2012.

As of December 2014, he has published over 160 scientific articles (including 17 in Science, Nature, Nature Group Journals and PNAS, and 40 in Physical Review Letters) and has given more than 280 invited talks (including over 140 at conferences) on his research. He has served as a General Member of the Aspen Center for Physics (since 2009) and on the Advisory Editorial Board of Journal of Physics - Condensed Matter (2002-2006), and has co-chaired a number of international conferences and workshops, including the 2007 International Conference on Strongly Correlated Electron Systems (SCES'07) and the 2014 KITP Program on Magnetism, Bad Metals and Superconductivity -- Iron Pnictides and Beyond.

Research Statement

Qimiao Si works in theoretical condensed matter physics, with an emphasis on quantum magnetism and superconductivity of strongly correlated electron systems.

Strongly correlated electron systems are at the forefront of condensed matter physics. Their theoretical description is a challenge that provides rich opportunities for creative research. The fundamental question is how the electrons are organized, and, in particular, whether there are principles that are universal among the various classes of these strongly correlated materials. The overarching goal of the group's research is to seek such principles of universality. Along the way, it is also fascinating to explore the diversity of the phenomena that result from electron correlations.

One area of Prof. Si's current interest is quantum criticality. He and his collaborators have advanced a by now well-known theory of local quantum criticality. Developed in the context of magnetic heavy fermion metals, which is a prototype system for quantum phase transitions, this theory features the "beyond-Landau" physics of critical Kondo destruction. A related topic of his recent research addresses novel phases that emerge in the vicinity of quantum critical points. He has also been interested in quantum critical physics in a variety of other contexts.

Another focus of Prof. Si's current research concerns iron-based superconductors. One important aspect of the work is to address the bad-metal behavior in the normal state, which is attributed to a proximity to delocalization-localization transition. This line of consideration has opened up studies on orbital-selective Mott phenomena. A corollary of this approach is that magnetism is primarily driven by J1-J2 interactions, a notion that he and his collaborators have pioneered. This approach has led them to theoretically predict a magnetic quantum critical point in iso-electronically tuned iron pnictides, which has been verified by extensive recent experiments. Finally, the implications of such magnetic interactions for the unconventional superconductivity is being studied; a recent work along this direction has shown how high Tc superconductivity may develop in the iron chalcogenides with seemingly unfavorable Fermi-surface conditions.

A variety of other topics in correlated electron systems are of interest to the group. These range from non-Fermi liquid behavior, quantum entanglement in many-body systems, cuprate superconductors, disordered and interacting electronic systems, metal-insulator transitions, out of equilibrium behavior of electronic systems, spin transport, and the probe of spin-charge separation.

"The new iron chalcogenide (K,Tl)FexSe2: pairing strength and symmetries, and some general lessons about iron pnictides", Theoretical and Experimental Magnetism Meeting, Rutherford Appleton Laboratory, UK, June 16-17, 2011.

"The new iron chalcogenide (K,Tl)FexSe2: pairing strength and symmetries, and some general lessons about iron pnictides", International Institute of Physics (IIP) Workshop on Superconductivity, Natal/RN, Brazil, May 16-30, 2011.

"Unconventional Superconductivity and Electron Correlations", Aspen Center for Physics Summer Workshop -- A New Century of Superconductivity: Iron Pnictides and Beyond, Aspen, CO, June 30, 2011.

"Phenomenological Aspects of Local Quantum Criticality." Fifth International Symposium on Advanced Science Research --Advances in the Physics and Chemistry of Actinide Compounds, JAERI Tokai, Ibaraki, Japan (cancelled due to Hurricane Rita). (Sept. 27-29, 2005)